The purpose of this project is the development of a non-invasive method of measuring tissue blood flow by analysis of the spectrum of doppler scattered laser light. The prototype instrument has been greatly improved by a new analysis scheme, a two meter flexible fiber optic probe, and the use of a photodiode detection system. The linearity of the instrument in response to blood flow has been greatly improved and noise has been reduced so the instrument can resolve the instantaneous pulsatile flow of microcirculation. The instrument has been used to monitor blood flow in normal individuals and Clinical Center patients. Preliminary studies of the vascular changes of Sickle Cell Patients and Muscular Dystrophy Patients have been initiated.